1. Field of the Invention
The present invention relates to an implantable measuring probe, and more particularly, to an ultrasonic probe for measuring the flow velocity of blood in natural blood vessels or replacement blood vessels of humans and animals.
2. Description of the Related Art
Implantable ultrasonic probes of the type mentioned above are already known for measuring the flow velocity of blood and have a piezoelectric crystal of approximately circular or quadratic shape (U.S. Pat. No. 4,947,854). As the irradiating and receiving surface of the piezoelectric crystal in the known ultrasonic probes is relatively small in comparison to the inner cross-section of the blood vessel and it cannot always be ensured in operations that this surface on the probe head is positioned with respect to the blood vessel in such a manner that that cross-section of the blood vessel essential for the measurement is irradiated with certainty, considerable measuring errors can occur with the known ultrasonic probes. This is particularly the case when the maximum flow velocities in the center of the blood vessel are not detected with the ultrasonic probe. This danger is of considerable significance in practice. Signal optimization problems in the implantation of the conventional ultrasonic probes can lead the surgeon to fix the probe too strongly to the vessel or its surroundings, which increases the danger of injuries and/or secondary bending of the blood vessels. Additionally, these measures are of often connected with relevant time losses during the operation.